The background of the invention will be set forth in two parts.
1. Field of the Invention
This invention relates to automatic machine tool systems and more particularly to electrical component insertion machines to stuff printed circuit boards.
2. Description of the Prior Art
Machine tools having a movable workpiece support carriage have long been equipped with automatic means for controlling the position of the carriage to a predetermined position or to a predetermined sequence of positions relative to a particular portion of the machine.
In the past, these functions have been programmed by means of mechanical and electromechanical means such as cams, switches and the like. Later, electronic techniques were employed for more accurate positioning and more complicated and more numerous sequential positioning. However, many of these machines require elaborate and very expensive tooling and components in order to ensure accurate results. For example, some schemes utilize expensive laser beam generators, while others use photosensitive elements with precision-produced exactly-tensioned perforated tapes, such as described in U.S. Pat. Nos. 3,603,691 and 3,586,950, respectively. Further, with respect to the state of the art dealing with positioning of a workpiece and the like, reference may be made to such patents as U.S. Pat. No. 3,786,332 disclosing positioning apparatus for moving a workpiece only a very small distance but with high precision (microns) and uses a laser light source and piezoelectric ceramic or magnetostrictive elements as drives, the displacement being measured by four interferometers whose beams illuminate reflecting faces of a reference block which supports the workpiece.
Another elaborate positioning scheme is described in U.S. Pat. No. 3,739,247. Here is found a positioning device for setting an article in a predetermined position, the article being positioned having a referential pattern of predetermined shape formed on a surface thereof. The device includes reference pattern carrier means having a reference pattern whose base portion is substantially similar in shape to the referential pattern of the article. Means is provided to move the article in a plane and to a position where the referential pattern on the article and at least the base portion of the superimposed images of the two patterns are scanned by photoelectric converter means to convert such images into electrical signals which are detected to determine the extent of deviation between the two patterns and to generate an error signal to activate movement means to correct such deviation.
U.S. Pat. No. 3,590,356 is pertinent in this area in that it concerns a light sensitive servomotor control circuit including a voltage sensitive motor, the circuit including two light sensitive elements which receive equal amounts of light when another element which is controlled by the circuit is positioned properly. Undesired movement of the element results in changes in the light received by the light sensitive elements thereby resulting in a loss of their equality. The diodes form a part of a balanced circuit, across which the motor is connected. In the balanced position, both sides of the motor are at the same potential and it remains stationary. When the control circuit becomes unbalanced in response to changes in the light sensitive elements, the motor is connected across a potential difference and rotates in a direction dictated by the direction of the potential difference. Rotation of the motor in the correct direction corrects the position of the elements under control and simultaneously equalizes the light impinging upon the light sensitive elements and thereby balances the control circuit.
As can be seen, light beam generators and light beam detectors play a significant part in many of the above-noted systems. In fact most of the more recent developments in this field utilize light beams because better accuracy is generally available. For example, in U.S. Pat. No. 3,808,485 there is described apparatus for registering a first element relative to a movable second element whereby a movable member has an initial position and is adapted to be moved to a predetermined relative relationship to the desired portion of the first element. A light source and a light receiver are cooperably arranged relative to each other, and a light modulating means passes light from the source to the light receiver such that a varying light intensity is passed thereby to the light receiver at different positions.
Probably the most pertinent examples of techniques using the detection of light energy to determine desired alignment of a movable object with respect to a fixed reference, now known to the inventors, are the following:
U.S. Pat. No. 3,482,103 describes a system for indicating direction and magnitude of deviation from a desired path of travel of a movable device or vehicle along a predetermined reference line. A light source is affixed to the vehicle and a remotely located light collector means is aligned parallel to the path center line and receives light rays from the source which are parallel to the vehicle travel direction. A plurality of photocells are positioned symmetrically about the optical axis of the aligned light collector means, and the photocells are responsive to changes in relative illumination about the optical axis.
U.S. Pat. No. 3,723,013 involves an alignment system which utilizes intermediate photodectors having central apertures and a terminal photodector, each photodetector having four quadrants of active area, with their centers aligned on the axis of a laser beam, their output signals bring utilized to indicate alignment, or the degree of misalignment, of their centers with respect to the axis of the laser beam. Alternately, their output signals are utilized to drive servo systems that automatically move tables on which they are mounted into alignment.
U.S. Pat. No. 3,749,924 concerns a target position detecting device for a line or edge target, the device using a plurality of detector photocells and a plurality of receiver optic fiber bundles which transmit light reflected from discrete areas of the target to the detector photocells.
U.S. Pat. No. 4,025,785 describes a device for automatic focusing of a stereoscopic microscope which generates a beam of rays from a pulse light source, which beam is focused on the object to be observed, the rays reflected back from the object along the divided paths of the observation rays are deflected from those paths and directed to impinge on separate photoelectric detectors which convert axial shifts of the object plane with respect to the microscope into a directionally dependent electric signal which controls a focusing motor to move the microscope to compensate for such shifts.
A study of the above-noted references will show that most use a beam of light which is generated usually by an expensive and complicated laser generator. It should therefore be evident that a new technique which need only utilize a simple incandescent source which easily produces a simply focused light beam or beams to detect any misalignment of a workpiece with respect to a desired position would constitute a significant advancement of the art.